Polychlorinated hydrocarbons, such as carbon tetrachloride, chloroform, trichloroethylene, and tetrachloroethylene have been widely used as chemical intermediates, solvents for dry cleaning of clothing, in degreasing operations, and in a variety of other applications. Chlorinated hydrocarbons are very stable compounds and are relatively toxic at low levels. Groundwaters have become contaminated by chlorinated hydrocarbons from sources such as disposal facilities, chemical spills, and leaking underground storage tanks.
Due to this fact, chlorinated hydrocarbons have been accumulating in the environment, particularly in groundwaters. As a result, pollution of water by chlorinated hydrocarbons has become an important environmental problem and contaminated groundwaters represent a large portion of environmental remedial action plans throughout the world. This is partially due to the improved analytical techniques used for detection of chlorinated hydrocarbons in many water supplies.
It is known that chlorinated compounds can be degraded by reductive dechlorination, that is, replacement of chlorine substituents by hydrogen. Metallic elements, such as iron and zinc, have been used to degrade chlorinated organic compounds.
In the patent literature, patents are issued that use metals or metallic couples to degrade chlorinated organic compounds. Recently, researchers in Japan have reported on the degradation of 1,1,2,2-tetrachloroethane and trichloroethylene in aqueous solution in the presence of iron powder: Senzaki, T. and Y. Kumagai, "Removal of Chlorinated Organic Compounds from Wastewater by Reduction Process: II. Treatment of Trichloroethylene with Iron Powder" Kogyo Yosui, 1989, 369, 19-25. Gillham and O'Hannesin in their article "Metal-Catalyzed Abiotic Degradation of Halogenated Organic Compounds" IAH Conference on Modern Trends in Hydrogeology: Hamilton, Ontario, May 10-13, 1992, have confirmed Senzaki's results. Recently, Gillham received a U.S. Pat. No. 5,266,213, for his method for cleaning halogenated contaminants from groundwater. The process involves feeding contaminated groundwater through a trench containing a metal such as iron, under strict exclusion of oxygen, and over a lengthy period of time.
The above-mentioned metal systems show the reductive dechlorination of chlorinated hydrocarbons in aqueous solutions by iron metal under the exclusion of oxygen. An oxygen-free environment must be utilized for these reactions to proceed. A disadvantage of these systems is the formation of insoluble precipitates that block the pore spaces of an in situ iron wall or ex situ metal packed column.
There is a need for metal wall or column remediation processes that effectively clean-up aqueous solutions contaminated with chlorinated hydrocarbons that have oxygen present. There is also a need for a reactive wall or column process that will not be blocked by the formation of insoluble precipitates that form in the wall or column. There is a further need for a low maintenance system that extends the operational life of the reactive wall or packed column.